ftrace: Fix char print issue in print_ip_ins()

When ftrace bug happened, following log shows every hex data in
problematic ip address:
  actual:   ffffffe8:6b:ffffffd9:01:21

But so many 'f's seem a little confusing, and that is because format
'%x' being used to print signed chars in array 'ins'. As suggested
by Joe, change to use format "%*phC" to print array 'ins'.

After this patch, the log is like:
  actual:   e8:6b:d9:01:21

Link: https://lkml.kernel.org/r/20221011120352.1878494-1-zhengyejian1@huawei.com

Fixes: 6c14133d

 ("ftrace: Do not blindly read the ip address in ftrace_bug()")
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>